The UN on Monday condemned the attacks and authorised countries to assist Deby's government.

Sarkozy said on Tuesday that France would support the Chadian government militarily if necessary.

Deby's government refused a ceasefire with its opponents on Tuesday, saying it was not needed as the rebels had been "decimated". An alliance spokesman had offered an end to the fighting if the president stepped down.

Khartoum denies Chad's claim that the fighters are Sudanese and supported by the Sudanese government.

Mutasa said relations between the two countries were strained: "It has brought up old wounds with Sudan, with each previously accusing the other of funding rebel groups to destabilise each country."

By Tuesday evening the capital's streets were deserted.

The government made radio broadcasts saying it had expelled all rebels in the city and appealed for residents to return.

Rebels regrouping

However, Bernard Kouchner, the French foreign minister, said on French radio on Wednesday that rebels seemed to be regrouping outside Ndjamena.

"For the moment, it is President Deby who holds the capital, but 100 or 200 [rebel] vehicles appear to have regrouped east of Ndjamena," he said.

French warplanes have been flying reconnaissance missions over opposition positions.

In the same broadcast Avocksouma Djona, the Chadian health minister, appealed to doctors and nurses to return to Ndjamena to treat the injured.